JP3455193B2 - Auto tensioner - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autotensioner that applies appropriate tension to a timing belt of an automobile engine or a belt that drives a plurality of accessories.

[0002]

2. Description of the Related Art An automatic tensioner is used in a belt drive mechanism that transmits a driving force of an engine to a plurality of devices by a single endless belt, and applies an appropriate tension to the belt, and at the same time, the engine speed and load are Attenuates vibration of the belt caused by fluctuations. This ensures that the driving force of the engine is transmitted to each device.

Generally, an automatic tensioner has a base fixed to an engine block and the like, a swing arm swingably supported by the base, and a pulley attached to the tip of the swing arm and abutting on a belt. Prepare The oscillating arm is provided substantially coaxially with the oscillating axis of the oscillating arm and is rotationally biased in the direction in which the belt is tensioned by the torsional torque of the torsion coil spring that tries to elastically return in the direction in which the coil diameter increases. Appropriate tension is applied.

Further, the autotensioner is provided with a damping mechanism for damping the belt, for example, a friction member is provided between the swing arm and the base, so that when the swing arm swings following the belt tension fluctuations, friction is generated. A friction damping mechanism is provided to generate resistance or damping force to brake the swing.

In recent years, as engine performance has increased, fluctuations in engine speed and load applied to belts have increased, and belt tension fluctuations have also increased. Therefore, when the damping force is small, the fluctuation of the tension of the belt cannot be suppressed and the vibration of the belt is generated. Therefore, in order to improve the vibration damping performance of the auto tensioner, it is necessary to make the damping high. Especially, the damping force (first damping force) acting on the swing arm when the belt is tensioned is applied to the swing arm when the belt is relaxed. It is preferable to set the damping force to be larger than the acting damping force (second damping force).

In order to meet this demand, as a first conventional friction damping mechanism, a friction member is pressed against a swing arm or a base by a reaction force of a torsion torque of a torsion coil spring to generate a high friction resistance. It has been known. When the swing arm rotates in the belt loosening direction, the reaction force of the torsion torque becomes larger than that when the belt is rotated when the belt is tensioned, and the friction resistance increases as the reaction force increases. Therefore, the first damping force can be set larger than the second damping force. If the torsion torque of the torsion coil spring is set to be large, it is possible to increase the frictional resistance, that is, the damping force, which depends on the magnitude of the reaction force.

However, when the torsional torque is increased, not only the frictional resistance but also the pressing force on the belt increases, so that the belt tends to be stretched and worn. For this reason, the magnitude of the torsional torque is limited, and a high damping is naturally limited. Further, the first damping force becomes larger than the second damping force by urging the friction member with the torsion coil spring, but the change of the torsion torque depending on the rotation direction of the swing arm is not so large, and the first damping force is not so large. It is difficult to make a large difference with respect to the second damping force. Therefore, when the torsional torque is increased to increase the damping, not only the first damping force but also the second damping force is increased, and the timing of tensioning the belt is delayed.
There is also a problem that the so-called belt followability is reduced.

As a second friction damping mechanism, there is known a structure in which a friction member is pressed against a swing arm or a base by an urging member separate from a torsion coil spring to generate stable high friction resistance. . In this case, the magnitude of the frictional resistance depends on the urging force of the urging member and is not related to the torsion torque. Therefore, a large damping force can be obtained only by changing the urging force of the urging member without increasing the torsion torque. be able to. That is, as compared with the first friction damping mechanism, there is an advantage that high damping can be achieved without changing the torsion torque.

However, according to the second friction damping mechanism, a constant frictional resistance acts even if the swing arm rotates in either the belt tension direction or the belt slackening direction, so that the urging force of the urging member is applied. If it is increased, not only the first damping force but also the second damping force is increased as in the first friction damping mechanism. That is, with this configuration, it is difficult to make the first damping force and the second damping force significantly different from each other, and the problem that followability is lowered due to high damping is still unsolved. Further, as compared with the first friction damping mechanism, the number of parts and the number of assembling steps are increased, which causes another problem that the manufacturing cost is increased.

[0010]

As described above, in the above-mentioned two types of friction damping mechanisms, it is necessary to improve both the vibration damping performance of the auto tensioner and to keep the belt following property well. Could not be satisfied at the same time.

The present invention has been made in view of the above problems, and it is an object of the present invention to improve the vibration damping performance without lowering the followability of the automatic tensioner.

[0012]

SUMMARY OF THE INVENTION An autotensioner according to the present invention has a pulley that comes into contact with a belt, and a swinging portion that has a pulley attached to one end and a cylindrical portion that is rotatably supported inside a bottomed cylindrical base. An auto tensioner equipped with a moving arm and a torsion coil spring that urges the swinging arm to rotate in a belt tension direction relative to the base. The torsion coil spring is mounted eccentrically to the axis of the base. At the same time, the swing arm is supported by the base so as to be relatively displaceable, so that the first damping force acting on the swing arm when the belt is tensioned is
It is characterized in that it is relatively larger than the second damping force acting on the swing arm when the belt is relaxed. As a result, the vibration damping performance is improved and the followability to the belt is improved.

In the above automatic tensioner, the swing arm is attached to the base so as to be movable in the radial direction. Further, the torsion coil spring is eccentrically attached to the base.

The autotensioner further includes a friction member interposed between the outer peripheral surface of the cylindrical portion of the swing arm and the inner peripheral surface of the base, and provided over at least 180 degrees around the axis of the base. A part of the cylindrical portion is pressed and urged by the torsion coil spring against the friction member. As a result, a large frictional force can be generated.

In the automatic tensioner, the magnitude of the first damping force is preferably 1.5 to 3.5 times the magnitude of the second damping force.

The friction member used in the auto tensioner may be provided with a plurality of protrusions for distributing the load acting in the direction in which the torsion coil spring presses and urges the arm cylindrical portion. Wear and damage can be prevented.

The autotensioner may further include a damping member which is separate from the friction member. Specifically, the damping member engages with the swing arm so as to be relatively movable in the radial direction and frictionally slides with the base. However, a larger damping force can be set.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a diagram showing a belt drive mechanism to which an auto tensioner according to a first embodiment of the present invention is applied. The belt drive mechanism includes a single endless belt 10, which includes a drive pulley 12 mounted on the output shaft of an engine (not shown) and a driven pulley mounted on a plurality of devices, such as an air conditioner. It is wound around a pulley 14 for a conditioner, a pulley 16 for a power steering device, and a pulley 18 for an alternator. Drive pulley 12
When is rotated, the belt 10 is rotated clockwise in the figure,
The rotational driving force is transmitted to the pulleys 14, 16 and 18 of each device.

The automatic tensioner 20 includes a drive pulley 12
In particular, the belt 10 is disposed behind the drive pulley 12 where the belt 10 is most slack in the belt rotation direction, and the pulley 22 of the auto tensioner 20 rotates relative to the back surface of the belt 10, that is, the outer peripheral side while contacting the belt 10. The swing arm 24 rotationally urges the pulley 22 in the direction of the arrow A in which the belt 10 is tensioned, so that the belt 10 is always given an appropriate tension.

When the belt 10 vibrates due to fluctuations in engine speed and load, this vibration is transmitted to the swing arm 24 via the pulley 22, and the swing arm 24 swings the swing axis L4.
Is swung about, and the pulley 22 is relatively moved between the first position shown by the solid line and the second position shown by the broken line. When the swing arm 24 swings, the swing arm 24 and the bushing 2
6 frictionally slides, and the generated frictional force acts as a damping force for braking the swing arm 24, and the relative movement of the pulley 22 is suppressed, and the vibration of the belt 10 is damped.

When the tension of the belt 10 suddenly increases and the pulley 22 is pushed toward the second position, the swing arm 24
Rotates in the clockwise direction (direction of arrow A), and at this time, a relatively large first damping force acts on the swing arm 24, and the pulley 22 moves slowly to effectively suppress the vibration of the belt 10. To do. On the other hand, when the belt 10 relaxes and the pulley 22 follows the belt 10 and moves toward the first position, the swing arm 24 moves in the counterclockwise direction (arrow B direction) about the swing axis L4. Rotate. At this time, a relatively small second damping force acts on the swing arm 24, and the pulley 22 quickly moves toward the belt 10 to tension the belt 10.

FIG. 2 is a sectional view of the automatic tensioner 20, and FIG. 3 is a plan view of the automatic tensioner 20 seen from the pulley 22 side. In FIG. 3, a part of the swing arm 24 is cut away and the pulley 22 is shown by a chain line.

The auto tensioner 20 is a base 3 integrally formed in a bottomed tubular shape from a metal material such as an aluminum alloy.
0, the base bottom surface portion 32 is fixed to an engine block (not shown). A base cylindrical portion 34 extends vertically from the outer peripheral edge of the base bottom surface portion 32, and the inside thereof is formed in a stepped shape. That is, two cylindrical surfaces having different diameters with the base axis L1 as the axis, that is, the opening side inner peripheral surface 34a and the bottom surface side inner peripheral surface 34b, and these two inner peripheral surfaces 34a and 34b.
And an annular seat surface 34c that connects the two. Inner surface 3 on the opening side
The diameter D1 of 4a is larger than the diameter D2 of the bottom side inner peripheral surface 34b, and the annular seat surface 34c is a plane having a constant width D3 and perpendicular to the base axis L1.

A circular base shaft hole portion 38 is formed in the center of the base bottom surface portion 32, and a stepped bolt 40 is inserted into the inside of the base shaft hole portion 38 from below in FIG. The swing arm 24 is swingably attached to the base 30 by the stepped bolt 40. When the belt 10 is not wound, the axis of the stepped bolt 40 and the swing axis L4 of the swing arm 24 substantially coincide with the base axis L1.

The swing arm 24 is integrally molded from a metal material such as an aluminum alloy, and has a bottomed cylindrical shape opening toward the base bottom portion 32. The arm bottom surface portion 242 is arranged inside the opening of the base 30, and a cylindrical swing shaft portion 244 extending toward the base bottom surface portion 32 is provided in the center thereof. The swing shaft portion 244 is open at both ends, and a female screw 244a is formed on the inner peripheral surface thereof. The female screw 244a is screwed into the male screw portion 42 formed at the tip of the step bolt 40, whereby the step bolt 40 and the swing arm 24 are integrally fixed.

The tip of the swing shaft portion 244 has a base shaft hole portion 38.
It goes inside and contacts the columnar portion 46 of the stepped bolt 40.
A part of the column portion 46 is arranged inside the base shaft hole portion 38 and has the same outer diameter as the swing shaft portion 244. A clearance is provided between the swing shaft portion 244 and the column portion 46 and the base shaft hole portion 38, and the swing arm 24 can relatively rotate without interfering with the base 30.

The head portion 44 of the stepped bolt 40 is a disc having an outer diameter larger than the inner diameter of the base shaft hole portion 38, and is locked to the base bottom portion 32. More specifically, a bolt accommodating portion 33, which is a cylindrical hole larger than the head portion 44, is formed in the base bottom surface portion 32. The bolt accommodating portion 33 communicates with the base shaft hole portion 38 and opens downward in FIG. . The head portion 44 is housed in the bolt housing portion 33 so as not to project from the base bottom surface portion 32. The swing arm 24 has a base axis L
A torsion coil spring 60 compressed in one direction urges the head 44 in a direction away from the base 30 (upward in FIG. 2), and the head 44 is locked to the bolt housing 33 via the thrust bearing 50. Thereby, the relative movement of the swing arm 24 along the base axis L1 direction is restricted.

The thrust bearing 50 is an annular member provided between the head portion 44 of the stepped bolt 40 and the bolt accommodating portion 33, and smoothly rotates the head portion 44 and the bolt accommodating portion 33 relative to each other. The thrust bearing 50 is molded from, for example, a synthetic resin material having self-lubricating property.

The inner diameter D12 of the base shaft hole portion 38 is formed slightly larger than the outer diameter D11 of the swing shaft portion 244 and the bolt columnar portion 46, and the inner diameter D14 of the bolt housing portion 33 is the outer diameter D13 of the bolt head portion 44. It is formed slightly larger. As a result, the swing arm 24 and the stepped bolt 40
Can smoothly rotate without interfering with the base 30,
Further, a slight displacement of the swing axis L4 with respect to the base axis L1 is allowed.

The swing arm 24 has a pulley bearing portion 248 that projects from the arm bottom portion 242 to the opposite side of the base 30, and the pulley 22 rotates via a ball bearing 70 on the radially outer side of the pulley bearing portion 248. Can be installed freely. The rotation axis L2 of the pulley 22 is parallel to the swing axis L4. The ball bearing 70 has a pulley bearing portion 248, which includes a mounting bolt 74 screwed and fixed in the pulley bearing portion 248 and a washer 72 interposed between the head of the mounting bolt 74 and the upper end surface of the ball bearing 70. Fixed to.

An arm cylindrical portion 246 extending toward the base bottom surface portion 32 is integrally provided on the outer peripheral edge of the arm bottom surface portion 244. The arm outer peripheral surface 246a is the base cylindrical portion 3
A cylindrical shape that is parallel to the opening-side inner peripheral surface 34a and faces the opening-side inner peripheral surface 34a at a predetermined distance, and is in contact with both surfaces over the entire axial direction between the arm outer-peripheral surface 246a and the opening-side inner peripheral surface 34a. Bushing 26 is provided.

The arm inner peripheral surface 246b has a diameter equal to the diameter D2 of the bottom surface side inner peripheral surface 34b of the base 30, and is the same as the bottom surface side inner peripheral surface 34b when the swing arm 24 is attached to the base 30. Located on the cylindrical surface. The base bottom surface portion 32 and the arm disk portion 242, the bottom surface side inner peripheral surface 34b of the base 30 and the arm inner peripheral surface 246b, the base shaft hole portion 38, and the swing shaft portion 244 form an outer diameter D2.
The annular chamber 100 is formed, and the torsion coil spring 60 is accommodated in the annular chamber 100.

The torsion coil spring 60 is a winding spring wound in the vicinity of the arm inner peripheral surface 246a, and one end portion 62 thereof is locked to the base bottom surface portion 32 and the other end portion 64.
Is locked to the arm bottom portion 242. The torsion coil spring 60 is twisted by a predetermined angle in the clockwise direction of FIG. 1 where the coil diameter is reduced, and is inserted in a state of being compressed in the direction of the base axis L1. Due to the torsional torque of the torsion coil spring 60 that elastically returns in the direction in which the coil diameter increases, the swing arm 24 is biased in the counterclockwise direction in FIG. 1 around the base axis L1 and is wound around the pulley 22. A predetermined tension is applied to the belt 10.

Since the torsion coil spring 60 is a winding spring, the reaction force of the torsion torque is the base axis L1.
It does not act evenly around, but the arm cylindrical portion 24
A part of 6 is pressed and urged by the torsion coil spring 60 toward a predetermined portion of the bushing 26 and the base cylindrical portion 34 which are radially outside. When the belt 10 is wound around the pulley 22 (see FIG. 3), the resultant force between the arm cylindrical portion 246 and the bushing 26 is the force of the belt 10 pressing the pulley 22 and the urging force of the torsion coil spring 60. Generates frictional force.

This will be described in detail with reference to FIGS. 4 and 5. Figure 4
5 is a plan view of the auto tensioner 20 around which the stationary belt 10 is wound, and FIG. 5 shows V passing through the base axis L1.
It is an end view in the -V line cross section. In addition, in FIG. 5, in order to avoid complication of the drawing, the swing arm 24, the base 3
Only 0 and the stepped bolt 40 are shown, and other configurations are omitted.

When the belt 10 presses the pulley 22, a load is applied to the step bolt 40 and the swing arm 24 in the axial load direction Y parallel to the straight line P that divides the belt winding angle γ into two equal parts. At this time, as shown in FIG. 5, a moment to tilt the swing axis L4 with respect to the base axis L1 with the base bottom surface 32 side as a fulcrum acts on the swing arm 24. As described above, clearances are provided between the swing shaft portion 244, the bolt columnar portion 46, and the base shaft hole portion 38, and between the bolt head portion 44 and the bolt accommodating portion 33. Due to the pressing force, the swing axis L4 slightly moves in the axis load direction Y relative to the plane perpendicular to the base axis L1 (FIG. 4), and at the same time slightly tilts toward the axis load direction Y and rotates strictly ( Figure 5).

In reality, since the bushing 26 and the thrust bearing 50 are interposed between the base 30 and the swing arm 24, they do not tilt so that they can be visually confirmed as shown in FIG. It is an extremely small value.

The torsion coil spring 60 biases the arm cylindrical portion 246 and the bushing 26 in the pressing direction Z and presses them against the base cylindrical portion 34. The pressing direction Z is substantially the same as the axial load direction Y, whereby the force with which the swing arm 24 presses the bushing 26 is the same as the biasing force of the torsion coil spring 60 in the pressing direction Z and the belt 1.
It is the sum of 0 and the pressing force in the axial load direction Y. The bushing 26 is strongly sandwiched by the arm cylindrical portion 246 and the base cylindrical portion 34, and a local force is concentrated especially on the pressing portion 26w indicated by hatching in FIG. Although the pressing direction Z does not have to strictly coincide with the axial load direction Y,
The range is preferably within ± 20 degrees around the base axis L1 with respect to the axial load direction Y (the counterclockwise direction is positive).

When the tension of the belt 10 increases with the belt 10 wound around, the pressing force of the belt 10 in the axial load direction Y increases, and the swing arm 24 relatively rotates in the clockwise direction in FIG. For torsion coil spring 6
When 0 is elastically deformed in the direction in which the coil diameter is reduced, the reaction force of the torsion torque increases, and along with this, the biasing force of the torsion coil spring 60 in the pressing direction Z also increases. Therefore,
The force that substantially matches the sum of the two, that is, the force that the swing arm 24 presses the pressing portion 26w of the bushing 26 outward in the radial direction is relatively large.

The frictional force generated between the swing arm 24 and the bushing 26 is the outer peripheral surface 246 of the swing arm which is the contact surface.
a and the bushing inner peripheral surface 26a are in proportion to the vertical load, that is, in proportion to the force pressing outward in the radial direction. As described above, when the belt tension increases, this vertical load becomes relatively large, so that a large frictional force is generated. Further, since the bushing 26 is strongly pressed against the opening-side inner peripheral surface 34a of the base 30, the bushing outer peripheral surface 2
A large frictional force is also generated between 6b and the inner peripheral surface 34a on the opening side. Therefore, when the swing arm 24 relatively rotates in the clockwise direction of FIG.
It acts on the swing arm 24 as a damping force, which causes a strong braking of the swing arm 24, the pulley 10 slowly follows the belt 10, and the vibration of the belt 10 is damped.

Further, as shown in the partially enlarged view of FIG.
If the swing axis L4 is tilted by an angle θ, the swing arm cylindrical portion 246 is not placed in parallel with the base cylindrical portion 34, but is tilted by the angle θ toward the axial load direction Y (in FIG. 6, it is directed to the lower left). To rotate). In other words, the pressing portion 26
In the vicinity of w, the distance between the opening-side inner peripheral surface 34a and the arm outer peripheral surface 246a gradually decreases toward the opening of the base 30. As a result, the pressing portion 26w is sandwiched more strongly by the inner peripheral surface 34a on the opening side and the outer peripheral surface 246a of the arm as the wedge is sandwiched toward the opening.
Therefore, an action such as a so-called wedge effect is added to the frictional resistance due to the pressing, and a large damping force can be stably exhibited. Note that, in FIG. 6, the degree of inclination is emphasized for the sake of explanation, and the inclination is not so much as actually shown.

On the other hand, when the tension of the belt 10 decreases, the force received from the belt 10 decreases, and the swing arm 24 relatively rotates in the counterclockwise direction in FIG. 60
Is elastically deformed in the direction of increasing the coil diameter, so that the torsion torque is reduced. As a result, the swing arm 24 relatively moves so that the swing axis L4 matches the base axis L1, and the force by which the swing arm 24 presses the bushing 26 in the pressing direction Z becomes extremely small. Further, since the degree of inclination of the swing arm 24 decreases and the opening-side inner peripheral surface 34a and the arm outer peripheral surface 246a face each other substantially in parallel, the pressing portion 26
The pinching force of w also becomes small, and the force applied to the bushing 26 is released. Therefore, the above-mentioned phenomenon such as the wedge effect is eliminated, and the frictional force is extremely reduced. in this way,
When the swing arm 24 relatively rotates counterclockwise in FIG. 4, the second damping force acting on the swing arm 24 is suppressed to a low level and the swing arm 24 is not braked so much. The conformability to the belt 10 is enhanced, and a predetermined tension is quickly applied to the belt 10.

As described above, according to the auto tensioner 20 of the present embodiment, the damping force can be relatively changed by displacing the swing arm 24 according to the rotation direction thereof, and the tension of the belt 10 is reduced. Vibration can be effectively suppressed without

Conventionally, the base (30) and the base (3
0), the space between the rocking arm (24) and the stepped bolt (40) that rotate relative to each other is filled with a synthetic resin bushing without any gap, and the rocking arm (24) is tilted or radially moved. The relative displacement of was not allowed. Therefore, the force pressing the bushing (26) outward in the radial direction is substantially constant regardless of the rotation direction of the swing arm 24, and it is difficult to make the first damping force and the second damping force largely different. . However, in the auto tensioner 20 of the present embodiment, the swing axis L4 is provided between the swing arm 24 and the stepped bolt 40 and the base 30.
The force for pressing the bushing 26 by the swing arm 24 can be largely changed only by providing the clearance for allowing the displacement of the first and second displacements, and the difference between the first and second damping forces can be increased. Such an auto tensioner 2
In the case of 0, it is not necessary to add a new part or manufacturing process as compared with the conventional case, and rather the manufacturing accuracy of the swing shaft portion 244 and the shaft hole portion 38 is not required, so that the manufacturing becomes easy.

Further, the wear amount of the pressing portion 26w of the bushing 26 is larger than that of other portions, but since the swing arm 24 is displaceable, even if the thickness of the pressing portion 26w is reduced, it is against the base 30. The swing arm 24 and the stepped bolt 40 can be slightly displaced in the direction in which the thickness is reduced (corresponding to the pressing direction Z in FIG. 4) by the biasing force of the torsion coil spring 60, and the bushing 26 and the swing arm 24 are constantly moved.
Can be closely attached. Therefore, stable frictional resistance can be obtained.

FIG. 7 is a perspective view of the bushing 26. The bushing 26 is, for example, a cylindrical member integrally formed by injection molding from a synthetic resin material containing polyphenylene sulfide as a main component. Polyphenylene sulfide is
It is a synthetic resin with a highly crystalline polymer structure, and has excellent heat resistance, abrasion resistance, strength, and dimensional stability, and also has a very low water absorption. Therefore, by applying polyphenylene sulfide to the bushing 26, the bushing 26
Can prevent an increase in frictional force even when exposed to water or salt water. In addition to the above polyphenylene sulfide, molybdenum for providing self-lubricating property, a heat stabilizer, an antioxidant, an ultraviolet deterioration inhibitor, etc. may be added to the material. Also, conventionally used polyether sulfone may be used as the main component of the material.

A part of the bushing 26 is fractured in the circumferential direction, and the fractured portion allows expansion and contraction due to temperature change. Further, a flange 262 having a constant width and extending inward in the radial direction is provided at an end of the bushing 26 on the base 30 side over substantially the entire circumference. The flange 262 is provided between the tip end surface of the arm tubular portion 246 and the annular seat surface 34c of the base 30 to prevent wear due to contact between the two and prevent the bushing 26 from falling off the base 30. The outer diameter of the bushing 26 is a natural length and the base cylindrical portion 34
The diameter is slightly larger than the inner diameter D1 and is inserted in the base cylindrical portion 34 in a state of being contracted in the radial direction. Therefore, the bushing 26 is moved to the base 3 by the force of expanding in the radial direction.
It is in close contact with the inner peripheral surface 34a of the opening 0. The bushing 26 includes the cylindrical portion 246 of the swing arm 24 and the base cylindrical portion 34.
Has an axial length substantially the same as the axial length H1 of
And the arm cylindrical portion 246 in close contact with each other over the entire axial direction.

A plurality of grooves 268 are formed on the inner peripheral surface 26a of the bushing 26 and extend over the entire axial direction.
The groove 268 plays a role of absorbing wear powder generated when the bushing 26 rubs against the swing arm 24 and releasing it to the outside. This prevents the inner peripheral surface 26a from being damaged by the abrasion powder. Although the cross-sectional shape of the groove 268 is a semicircle in this embodiment, it is not particularly limited to a semicircle. The groove depth is also not particularly limited, but if it is made too deep, bending will occur, and if it is made too shallow, wear debris will collect in the groove 268, so it is necessary to have an appropriate groove depth. Similarly, if the groove width is too large, the necessary frictional force cannot be obtained, and if the groove width is narrowed, wear powder accumulates in the groove 268, so it is necessary to set the groove width to an appropriate value.

The fractured portion of the bushing 26 is on the opposite side of the pressed portion 26w (see FIG. 3), which has the greatest wear, that is, in FIG.
Is located above and to the right. As a result, radial expansion due to wear is easy and stable frictional force can be obtained. In the present embodiment, the bushing 26 has a cylindrical shape that is partially broken, but it may be provided in a range where the swing arm 24 presses, and specifically, from the axial load direction Y around the base axis L1. It may be provided over a range of ± 90 degrees.

In the auto tensioner 20 of this embodiment, the diameter of the base 30 is relatively large with respect to its axial length, and the thin type is adopted, and the bushing 26 is provided outside the torsion coil spring 60. The diameter of the bushing 26 is relatively large, and the friction area with the swing arm 24 can be set large. Further, since the bushing 26 is in close contact with the arm cylindrical portion 246 over the entire axial direction, the friction area can be increased. Therefore, a relatively large frictional force can be obtained even if the rotation angle of the swing arm 24 is small. Furthermore, since the acting position of the frictional force can be set far from the swing axis L4 (or the base axis L1), the swing arm 24 can be effectively braked.

Since the pulley-side end portion 264 of the bushing 26 is exposed to the outside, it allows water or salt water to enter the interface with the base cylindrical portion 34 and the interface with the arm cylindrical portion 246, and the outer surface is protected from water and salt water. It has a structure that is easily exposed to salt water. However, since the bushing 26 is formed of a material containing polyphenylene sulfide as a main component, the frictional force does not increase even when it is exposed to water, and the smooth swing of the swing arm 24 is not hindered. Slip phenomenon and belt squeal phenomenon are prevented.

FIG. 8 is a plan view of the torsion coil spring 60 as viewed from the swing arm 24 side. The torsion coil spring 60 includes a spiral portion 6 having a diameter D4 in an unloaded state.
6 is provided. The number of turns of the spiral portion 66 is about 2.2. One end portion 62 locked to the base 30 extends linearly from the spiral portion 66, is on the spiral axis L3 side of the spiral portion 66, and is perpendicular to the spiral axis L3. The other end portion 64 locked to the swing arm 24 has the same configuration as the one end portion 62. On a plane perpendicular to the spiral axis L3, an angle α formed by a straight line K1 extending through the center of the one end portion 62 toward the bent portion 63 and a straight line K2 extending through the center of the other end portion 64 toward the bent portion 65.
Is about 60 degrees, but a range of 50-80 degrees is preferred.

FIG. 9 is a plan view of the state in which the torsion coil spring 60 is attached to the base 30 as seen from the swing arm 24 side. The torsion coil spring 60 is shown by hatching, and only one turn on the base 30 side is shown. The base bottom surface portion 32 is formed with two locking projections 322 and 324 that sandwich the one end portion 62. The first locking projection 322 has a lunar shape protruding inward from the base cylindrical portion 34, and the side surface 322 a on the plane thereof supports the one end 62 from the outside in the radial direction. The second locking protrusion 324 has an annular shape provided around the entire circumference of the base shaft hole 38, and has an outer peripheral surface 324 a facing the first locking protrusion 322.
In contact with the one end portion 62 from inside in the radial direction. A part of the outer peripheral surface of the second locking projection 324 projects radially outward in an arc shape, and the projected curved surface 324b contacts the bent portion 63 of the torsion coil spring 60. As described above, the one end portion 62 is locked to the base bottom surface portion 32, and in the locked state, the one end portion 62 is substantially parallel to the axial load direction Y.

The outer diameter D4 of the spiral portion 66 is larger than the diameter D2 of the annular chamber 100 to be housed, and in the state where the end portion 64 in which the one end portion 62 is locked to the base 30 is a free end and no load is applied, the spiral portion 66 is formed. The axis L3 does not coincide with the base axis L1,
It is eccentric to a position displaced to the lower left in the figure. Base axis L
The eccentric direction of the spiral axis L3 with respect to 1 is substantially the same as the axial load direction Y.

FIG. 10 is a plan view of the state in which the torsion coil spring 60 is attached to the swing arm 24 as seen from the base 30 side. In the drawing, the torsion coil spring 60 is shown by hatching, and only one turn on the swing arm 24 side is shown. On the arm bottom surface portion 224, there are a string-shaped third locking projection 243 protruding inward from the arm cylindrical wall 246, and a crescent-shaped fourth locking projection 245 provided on the back side of the pulley bearing portion 248. It is provided. Third locking protrusion 243
Supports the other end 64 of the torsion coil spring 60 from the outside in the radial direction, and the fourth locking protrusion 245 supports the bent portion 65, which is a connecting portion between the other end 64 and the spiral portion 66, from the inside in the radial direction. . As described above, the other end 64 of the torsion coil spring 60 is locked to the swing arm 24.

When assembling the automatic tensioner 20, first, the one end 62 of the torsion coil spring 60 is engaged with the base 30 fitted with the bushing 26 (first step). Since the spiral portion 66 cannot be accommodated in the base 30 when the other end portion 64 is a free end, the swing arm 24 is then put over the torsion coil spring 60 to cover the other end portion 64 with the third and fourth portions. The torsion coil spring 60 is twisted in a direction (clockwise direction in FIG. 9) in which the diameter of the spiral portion 66 is reduced by engaging the engagement protrusions 243 and 245 (second step) and rotating the swing arm 24 ( Third step). As a result, the outer diameter of the spiral portion 66 becomes smaller than the diameter D2 and can be accommodated in the annular chamber 100. afterwards,
The swing arm 24 is pressed toward the base 30 to compress the torsion coil spring 60 in the direction of the base axis L1 (fourth
Step), the stepped bolt 40 is screwed to the swing arm 24 in the compressed state, and the swing arm 24 is rotatably fixed to the base 30 (fifth step). Then, the pulley 22, the ball bearing 70, the washer 72, and the mounting bolt 7
4 is assembled (6th step). Through the above first to sixth steps, the auto tensioner 20 in the state shown in FIG. 2 is obtained.

Generally, the size of the base 30 accommodating the torsion coil spring 60 is determined by the size of the mounting space allocated to the auto tensioner 20,
Torsion coil spring 6 according to the size of the base 30
The size of 0, that is, the limit values of the outer diameter and the axial length are naturally determined. In recent years, the size of the base 30 tends to become smaller as the space for mounting the auto tensioner 20 becomes smaller as the engine becomes smaller. On the other hand, the load on the belt 10 tends to increase as the engine becomes more sophisticated, and the auto tensioner 20 is also required to increase the output load to be applied to the belt 10, that is, increase the spring torque. However, the spring torque is the torsion coil spring 6
Since the coil thickness is 0, the output load is reduced if the base 30 is made small, and the base 30 must be made large if the output load is set high.

Conventionally, in the torsion coil spring, a torsion coil spring having an outer diameter smaller than the inner diameter of the base or the swing arm is housed in the base so as not to come into contact with the base or the swing arm, and is twisted by a predetermined angle. The swing arm was urged by assembling it. However, since the outer diameter of the torsion coil spring is further reduced by twisting, the gap between the torsion coil spring and the base is increased, and the accommodation space (annular chamber 100) cannot be used effectively. Therefore, the present applicant pays attention to the fact that the outer diameter of the torsion coil spring is reduced by being twisted, and the torsion coil spring 60 having an outer diameter D4 which is somewhat larger than the diameter D2 of the annular chamber 100 is twisted and then accommodated. A method of effectively utilizing the annular chamber 100 has been found. As a result, even if the volume of the annular chamber 100 is the same as the conventional one, the torsion coil spring 60 longer than the conventional one can be used, and the output load can be increased without increasing the size of the base 30 and the swing arm 24. Also, the number of assembly steps is the same as the conventional one.

This configuration is effective when applied to a thin auto tensioner 20 having an outer diameter relatively larger than the axial length as in this embodiment. This is because, when the outer diameter is increased without changing the axial length of the torsion coil spring 60, the larger the diameter of the torsion coil spring 60 is, the larger the increase of the coil length is.
In the case of a thin type, since the axial length of the base 30 is short, it is extremely easy to engage the one end of the torsion coil spring 60 with the base 30 while accommodating the torsion coil spring 60 in a tilted manner. Even if the twist angle is the same, the reduction of the outer diameter is large, so that the diameter can be sufficiently reduced only by twisting.

FIG. 11 is a diagram comparing the torsion coil springs 60 before and after the third step (twisting step). The twisted coil spring 60 before being twisted is shown by a broken line, and the twisted coil spring 60 after being twisted is shown by a solid line.

With one end 62 locked, the other end 6
4 is twisted clockwise about the axis L1 by a twist angle β, the outer diameter of the torsion coil spring 60 is D4.
To D5. At this time, a part of the spiral part 66 away from the one end part 62, particularly a part far from the bent part 63 locked to the base 30, is moved to the base axis L1 side, and the spiral axis L3 is changed from the initial position indicated by a white circle. , Is eccentric to a position indicated by a black circle near the locked bent portion 63. The spiral axis L3 after the assembly of the auto tensioner 20 is eccentric to the base axis L1 in the upper right direction in the figure, that is, in the direction substantially opposite to the axial load center Y.

The outer diameter D5 of the spiral portion 66 after twisting is set to a value smaller than the diameter D2 of the annular chamber 100. Specifically, the outer peripheral portion of the spiral portion 66 is the inner peripheral surface of the arm inner surface 246b or the inner peripheral surface of the bottom surface. It is set to a value smaller than the diameter D2 by a clearance for separating the surface 34b so as not to interfere with the surface 34b.

Thus, the torsion coil spring 60
Is accommodated in the base 30 in an eccentric and twisted state, whereby the swing arm 24 is pushed in the pushing direction Z substantially coincident with the axial load direction Y, and the swing arm 24 is tilted. Therefore, the force with which the swing arm 24 presses the bushing 26 at the time of belt tension can be increased, and the damping effect can be enhanced by setting the first damping force to an extremely large value. The process of assembling the torsion coil spring 60 is the same as the conventional process and is easy.

The eccentric position and the amount of eccentricity of the spiral shaft center L3 after the assembly of the automatic tensioner 20 are as follows: the angle α formed by the end portions 62 and 64, the torsion angle β, the locking projections 322 and 324 of the base 30, and the outer peripheral surface 324b. Is determined by the position of. These values and positions, the diameter D2 of the annular chamber 100 accommodating the torsion coil spring 60, the number of windings of the torsion coil spring 60, and the outer diameter D4 of the natural length are not particularly limited to this embodiment, It is needless to say that the design can be changed to a value and a position where the damping performance of the tensioner 20 can be most effectively exhibited.

The characteristics of the automatic tensioner 20 will be described with reference to the graph of FIG. FIG. 12A is a graph showing the output characteristics of the auto tensioner 20 in which the bushing 26 is removed and only the torsion coil spring 60 is provided. In this graph, the horizontal axis represents the rotation angle of the swing arm 24 from a predetermined initial position, and the vertical axis represents the output load of the auto tensioner 20.

The swing arm 24 is rotated from the initial position by the rotation angle D1.
When rotated up to, that is, in the normal rotation, only the torsional torque that proportionally increases acts on the swing arm 24, so that the normal rotation load Ca output from the auto tensioner 20 increases proportionally as the rotation angle increases. When the swing arm 24 rotated to the rotation angle D1 returns to the initial position due to the torsion torque of the torsion coil spring 60, that is, at the time of reverse rotation, the torsion torque is proportionally reduced, and therefore the reverse rotation load Cb output from the auto tensioner 20 is the rotation angle. Decrease in proportion to the decrease of. The straight lines showing the forward load Ca and the reverse load Cb substantially coincide with each other, and the inclinations of the straight lines indicate the torsion coil spring 60.
It corresponds to the torsion spring constant of.

FIG. 12B is a graph showing the output characteristic of the auto tensioner 20 provided with both the bushing 26 and the torsion coil spring 60. For reference, the output characteristics (normal rotation load Ca and reverse rotation load Cb) of the torsion coil spring 60 alone are shown by a chain line.

Forward load T when the bushing 26 is provided
a is larger than the normal rotation load Ca of the torsion coil spring 60 alone by a load Pa (Pa = Ta-Ca),
The load Pa corresponds to the frictional resistance generated by the bushing 26, that is, the first damping force. Also, bushing 2
The reverse rotation load Tb when 6 is provided is larger than the reverse rotation load Cb when the torsion coil spring 60 is used alone.
= Tb-Cb), the load Pb is the frictional resistance generated by the bushing 26, that is, the second damping force.

As shown in FIG. 12 (b), the second damping force Pb is substantially constant from the initial position to the angle D1, and the first damping force Pa gradually increases as the rotation angle increases. It is always larger than the second damping force Pb. As described above, by providing the bushing 26, it is possible to apply the damping force Pa or Pb having different magnitudes depending on the rotation direction of the swing arm 24. The ratio of the magnitudes of the first damping force Pa and the second damping force Pb is P
a: Pb = 1.5 to 3.5: 1. This ratio can be set to an arbitrary value by changing the friction coefficient of the bushing 26 and the outer diameter of the arm cylindrical portion 246.

As described above, in the auto tensioner 20 of the present embodiment, the clearance is provided between the swing arm 24 and the stepped bolt 40 and the base 30 to allow the relative displacement of the swing arm 24, and A configuration is provided in which the torsion coil spring 60 is eccentric to press the swing arm 24 in a pressing direction Z that substantially matches the axial load direction Y. As a result, when the swing arm 24 moves in the A direction (FIG. 1), the torsion coil spring 60 is twisted, the swing arm 24 is relatively displaced in the axial load direction Y, and the swing arm 24 moves to the bushing 26. It is strongly pressed and the clockwise rotation of the swing arm 24 is braked by the relatively large first damping force. On the other hand, when the swing arm 24 moves in the B direction, the twist of the torsion coil spring 60 is returned, and the swing arm 24 moves to the bushing 2
The second damping force is reduced away from 6, and the swing arm 24 can easily rotate counterclockwise. That is, the vibration damping performance of the auto tensioner 20 can be improved, and the followability is extremely good.

A second embodiment of the auto tensioner according to the present invention will be described with reference to FIGS. 13 and 14. FIG.
[Fig. 6] is a plan view of the auto tensioner, showing only a part of the bushing and the swing arm attached to the base. FIG. 14 is a perspective view showing the bushing partially broken away. The autotensioner of the second embodiment has the same configuration as that of the first embodiment except that the shape of the bushing is different. The same components are designated by the same reference numerals and description thereof is omitted.

The bushing 426 of the second embodiment is a semi-cylindrical member provided over the range of 180 degrees around the base axis L1 and its center in the circumferential direction is on the axial load direction Y. That is, the bushing 426 is ± 90 from the axial load direction Y.
The arm outer peripheral surface 246a is slidably contacted over a range of degrees.

Although the bushing 26 of the first embodiment has a cylindrical shape, the portion that receives the most load is actually the axial load direction Y.
Is a pressing portion 26w (FIG. 4) located at the position (2) and receives a load only within a range of approximately ± 90 degrees from the axial load direction Y. Therefore, the bushing 26 is provided on the opposite side of the arm outer peripheral surface 24.
It is separated from 6a, and no frictional force is generated. From this, in the third embodiment, only the semi-cylindrical portion extending over the range of ± 90 degrees from the axial load direction Y required for frictional sliding is used as the bushing 426, and even with such a shape, the first embodiment is used. The same effect as the embodiment can be obtained. Although not shown, it is preferable that a detent for positioning the bushing 426 is provided on the bushing 426 or the base 30. As described above, according to the second embodiment of the present invention, similarly to the first embodiment, it is possible to improve the vibration damping performance without lowering the followability, and further, the number of materials is smaller than that of the first embodiment.

A third embodiment of the auto tensioner according to the present invention will be described with reference to FIGS. 15 and 16. Figure 15
[Fig. 6] is a plan view of the auto tensioner, showing only a part of the bushing and the swing arm attached to the base. FIG. 16 is a perspective view showing the bushing partially broken away. The autotensioner of the third embodiment has the same configuration as that of the first embodiment except that the shape of the bushing is different. The same components are designated by the same reference numerals and description thereof is omitted.

The bushing 526 is provided with two protrusions 552 and 554 that project inward in the radial direction.
46a is in close contact with the bushing 526 only at the protrusions 552 and 554, and does not contact other parts. Protrusion 55
2 and 554 are provided over the entire axial direction of the bushing 526, and are 45 degrees apart from the axial load direction Y (pressing direction Z) in the circumferential direction. The force pressing the bushing 526 when the belt 10 is wound is concentrated in the axial load direction Y. However, in the third embodiment, the protrusions 552 and 554 receive a load, and the load is dispersed. Further, since the projections 552 and 554 are positioned at 45 degrees with respect to the axial load direction Y, the load applied to each is 1 / √2 of the load applied in the axial load direction Y.
Therefore, according to the third embodiment of the present invention, similarly to the first embodiment, not only the damping performance can be improved without lowering the followability, but also the early damage and early wear of the bushing 526 can be prevented, and the auto tensioner 20 can be prevented. The durability of can be improved.

The angle formed by the protrusions 552 and 554 with respect to the axial load direction Y is not limited to the above-mentioned 45 degrees, and may be 30 degrees.
It may be 60 degrees or 60 degrees. Also, the bushing 52
Although 6 is a cylindrical member, it may be a semi-cylindrical member as in the second embodiment.

A fourth embodiment of the automatic tensioner according to the present invention will be described with reference to FIGS. 17 and 18. FIG. 17
FIG. 18 is a sectional view of the auto tensioner, and FIG. 18 is a perspective view of the bushing. The auto tensioner of the fourth embodiment has the same configuration as that of the first embodiment except that the shapes of the bushing and the thrust bearing are different and that a damping mechanism is further provided. For the same configuration, 600 is added to the reference numeral. The description will be omitted. The configuration of the pulley and its periphery is indicated by broken lines.

In the automatic tensioner 620 of the fourth embodiment, the base bottom surface portion 632 and the arm disk portion 84.
2, the bottom surface-side inner peripheral surface 634b of the base 630, the arm inner peripheral surface 846b, the base shaft hole portion 638 and the swing shaft portion 844, the annular chamber 700 is formed, and the torsion coil spring 660 is formed in the annular chamber 700. Not only is the damping mechanism housed.

In the first embodiment, the frictional resistance is set to the swing arm 2
Although only the bushing 26 was applied to the member No. 4 as described above, there are cases where a sufficient damping force cannot be obtained only by the bushing 26. In order to meet this requirement, the fourth embodiment is further provided with another damping mechanism that imparts frictional resistance to the swing arm 624, and thereby a high damping force is generated.

In this damping mechanism, the second cylindrical portion 702 integral with the base 30, the cylindrical damping member 704 attached to the swing arm 624, and the damping member 704 are pressed from the inside toward the second cylindrical portion 702. And a ring spring 706 that operates. These configurations are patent second
Since it is the same as the damping mechanism shown in No. 981433, detailed description thereof will be omitted. The damping member 704 rotates integrally with the swing arm and frictionally slides on the second cylindrical portion 702. The frictional force generated at this time is the ring spring 706.
Proportional to the urging force of. Not only the frictional force generated in the bushing 626 but also the frictional force generated in the damping member 704 acts on the swing arm 624, so that the swing arm 624 can apply strong braking.

A mounting hole 710 for the damping member 704;
Mounting pin 7 of swing arm 624 that engages with mounting hole 710
A clearance allowing relative displacement of the swinging arm 624 is provided between the swinging arm 62 and the swinging arm 62.
It is possible to prevent the damping member 704 from being distorted due to strain when it is displaced, and it is possible to generate a stable frictional force regardless of the displacement of the swing arm 624.

The thrust bearing 650 is not an annular member,
It is a tubular member provided with a flange. Thrust bearing 650
Is fitted into the base shaft hole 638 without any clearance, and faces the cylindrical portion 646 of the stepped bolt 640 inserted through the inside with a clearance. Regarding the direction of the base axis L1, the thrust bearing 650 has the bolt head 644.
And it is clamped by the base bottom surface portion 632 without a gap.
As a result, relative displacement of the swing arm 624 is allowed, and further wear due to mutual interference between the base 30 and the stepped bolt 40, both of which are made of a metal member, can be prevented. The cylindrical portion of the thrust bearing 650 may be formed in a tapered shape whose diameter decreases toward the swing arm 624 side.

The bushing 626 has a base bottom portion 632.
Has a tapered cross section in which the diameter gradually decreases toward
A flange 862 extending inward in the radial direction is integrally formed at one end of the cylindrical portion over about 180 degrees. The flange portion 862 is formed by the base 30 and the swing arm cylindrical portion 844.
Is axially sandwiched between the bushing 626 and the tip surface of the bushing 626.
Not only does it prevent falling off of the base 30 but also has a function of preventing rotation in the circumferential direction. Although not shown, the annular seating surface 634c of the base 630 is formed in a stepped shape for locking the flange 862 in the circumferential direction. The flange 862 is preferably provided over a range of ± 90 degrees from the axial load direction in which the swing arm 624 has the largest inclination in order to prevent the swing arm 624 from extremely tilting.

A flange 720 covering the bushing 626 is formed over the entire circumference of the swing arm bottom surface portion 842. The flange 720 covers the upper end surface of the bushing 626 and further extends to the opening surface of the base cylindrical portion 634. It extends diagonally downward in the figure. The flange 720 protects the upper end surface of the bushing 626 from the outside, and prevents dust, water, salt water, and the like from entering the surface of the bushing 626. Furthermore, the damping member 704 provided in the annular plate member-shaped chamber 700 is simultaneously protected from dust, water, salt water, and the like.

As described above, also in the auto tensioner 620 of the fourth embodiment, the damping force is relatively changed by displacing the swinging arm, similarly to the first embodiment, without lowering the followability. The vibration damping performance can be improved. Furthermore, by providing the damping member 704, a high damping force can be set. Also,
A thrust bearing 650 is provided between the shaft hole 638 and the bolt 640 to cover the end face of the bushing 626.
By providing 0, the base 30 and bushing 626
It is possible to prevent early damage and wear of the auto tensioner 6
The durability of 20 can be improved.

[0087]

EXAMPLES Next, a durability test of the auto tensioner 20 was conducted to examine changes in the damping force and the ratio of the first and second damping forces with the passage of time. FIG. 19 is a layout diagram showing the state of the durability test, and FIG. 20 is a graph showing the measurement results of the auto tensioner in the initial state.

In the durability test, the auto tensioner (20)
Remove the bushing 26 from the torsion coil spring 60.
The output load when only the sole was provided and the output load when the bushing 26 of the first embodiment (see FIG. 2) was provided were measured in the initial state immediately after assembly. Further, a separate auto tensioner (20) having the same structure as the auto tensioner (20) used for the measurement in the initial state was used for the belt transmission mechanism shown in FIG. 1 for 180 hours, and the fatigue state after 180 hours had passed. The output load when only the torsion coil spring 60 was provided and the output load when the bushing 26 was provided were measured.

In measuring the output load, the V-shaped block 90 is brought into contact with the side surface of the pulley 22 and the pulley 22 is pressed in one direction to rotate the swing arm 24 forward, and then the V-shaped block 90 is returned. The swing arm 24 is rotated in reverse, and the load that the V-shaped block 90 receives from the pulley 22, that is, the output load of the auto tensioner 20 is measured by the detector 92 attached to the V-shaped block 90.

Table 1 shows the automatic tensioner (2
0), the normal rotation load and the reverse rotation load when the swing arm 24 is in the first position (rotation angle 28 degrees) shown by the solid line in FIG. 19 and the second position (rotation angle 40 degrees) shown by the broken line in FIG. And the first and second damping forces Pa and Pb at each position, and the ratio (P
a / Pb).

[0091]

[Table 1]

Table 2 shows the auto tensioner (2
0), the results of measuring the forward rotation load and the reverse rotation load when the swing arm 24 is at the first position and the second position, and the first and second damping forces Pa at the respective positions.
And Pb and the ratio of both (Pa / Pb) are shown. The dimensions and material of the bushing 26 used here, that is, the friction coefficient and the outer diameter of the swing arm 24 (arm cylindrical portion 246) are
It is the same as the auto tensioner measured in the initial state.

[0093]

[Table 2]

The experimental results shown in the above two tables are examples, and according to the above experimental results and other experimental results for the auto tensioner in which the friction coefficient of the bushing 26, the outer diameter of the arm 24, the durability time, etc. are changed, The first damping force Pa is always larger than the second damping force Pb, and the ratio Pa / Pb thereof is in the range of 1.5 to 3.5, and at both the first position and the second position, after fatigue. It turns out that this ratio relationship always holds even if there is.

[0095]

As described above, in the autotensioner of the present invention, the swinging arm is displaced in accordance with the rotational direction to change the damping force relative to each other, whereby the followability of the autotensioner is not deteriorated. There is an advantage that the vibration damping performance can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a belt drive mechanism to which an auto tensioner of the present invention is applied.

FIG. 2 is a sectional view showing a first embodiment of an auto tensioner according to the present invention.

FIG. 3 is a plan view of the auto tensioner shown in FIG. 2 as viewed from a pulley.

FIG. 4 is a plan view of an auto tensioner having a stationary belt wound around it.

5 is an end view of the auto tensioner taken along the line VV in FIG. 4, showing only the base, the swing arm, and the stepped bolt.

6 is a partially enlarged cross-sectional view of FIG. 2 showing a state where a bushing is sandwiched by a base and a swing arm.

FIG. 7 is a perspective view of the bushing shown in FIG.

FIG. 8 is a plan view of the torsion coil spring shown in FIG.

FIG. 9 is a plan view showing a state where an end of a torsion coil spring is attached to a base.

FIG. 10 is a plan view showing a state where an end portion of a torsion coil spring is attached to an arm.

FIG. 11 is a diagram showing a dimensional difference before and after assembling a torsion coil spring.

FIG. 12 is a graph showing the output characteristics of the auto tensioner shown in FIG. 1 when the bushing is removed and when the bushing is provided.

FIG. 13 is a view showing the second embodiment of the automatic tensioner according to the present invention, and is a view showing a part of the bushing and the swing arm attached to the base.

FIG. 14 is a perspective view showing the bushing of FIG. 13 with a part thereof cut away.

FIG. 15 is a view showing the third embodiment of the automatic tensioner according to the present invention, and is a view showing a part of the bushing and the swing arm attached to the base.

16 is a perspective view showing the bushing of FIG. 15 partially broken away.

FIG. 17 is a sectional view showing a fourth embodiment of the auto tensioner according to the present invention.

FIG. 18 is a perspective view showing the bushing of FIG. 17 with a part thereof cut away.

FIG. 19 is a diagram showing how the output load of the auto tensioner is measured.

FIG. 20 is a diagram showing a measurement result of an output load of the auto tensioner.

[Explanation of symbols]

20, 620 Auto tensioner 30, 630 Base 34, 634 Base cylindrical portion 24, 624 Swing arm 246, 646 Arm cylindrical portion 26, 426, 526, 626 Bushing (friction member)

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F16H ^7/ 00-7/24

Claims (11)

(57) [Claims] 1. A pulley that is in contact with a belt, and a swinging arm that has the pulley attached to one end thereof and that has a cylindrical portion that is rotatably supported inside a bottomed cylindrical base.
An auto tensioner having a torsion coil spring for biasing the swing arm to rotate in a direction in which the belt is tensioned with respect to the base, wherein the torsion coil spring is eccentrically attached to an axis of the base. together is, by the swing arm is supported movably in the radial direction against the base, first damping force acting on the swing arm during tensioning of the belt, the oscillating during relaxation of the belt An automatic tensioner characterized in that it is relatively larger than the second damping force acting on the moving arm. 2. The automatic tensioner according to claim 1, wherein the magnitude of the first damping force is 1.5 to 3.5 times the magnitude of the second damping force. 3. A friction member interposed between the outer peripheral surface of the cylindrical portion of the swing arm and the inner peripheral surface of the base, and provided over at least 180 degrees around the axis of the base. The auto tensioner according to claim 1, further comprising: a portion of the cylindrical portion that is pressed against the friction member by the torsion coil spring. 4. The auto according to claim 3 , wherein the friction member is provided with a plurality of protrusions for distributing a load acting in a direction in which the torsion coil spring presses and urges the cylindrical portion. Tensioner. 5. A damping member separate from the friction member is further provided, and the damping member engages with the swing arm so as to be movable in the radial direction and frictionally slides with the base. The automatic tensioner according to claim 3 . 6. The friction member is polyphenylene sulph.
Specially made from a material whose main component is a guide resin
The automatic tensioner according to claim 3, which is a characteristic. 7. The friction member is partially formed in a circumferential direction.
The auto according to claim 3, which is broken.
Tensioner. 8. The swing arm of the friction member
Multiple grooves are formed on the friction sliding surface of the
The auto tensioner according to claim 3, wherein
Na. 9. The shaft of the cylindrical portion of the base is the friction member.
Has an axial length substantially equal to the length, and the cylindrical portion of the base and the
Close contact with the cylindrical part of the swing arm over the entire axial direction.
The autotensioner according to claim 3, wherein: 10. A rotary unit that rotates the swing arm on the base.
An oscillating shaft portion that rotatably supports is provided, and the oscillating shaft portion is
When entering the shaft hole provided on the bottom of the base,
A clearance between the swing shaft and the shaft hole.
It has, The auto tensi of Claim 1 characterized by the above-mentioned.
Yona. 11. The axial center of the torsion coil spring is
About the pressing force of the belt with respect to the axis of the base,
Characterized by being mounted eccentrically in the axial load direction
The automatic tensioner according to claim 1.